With iOS 9, Apple made numerous changes and improvements to its frameworks, including some significant updates to the way URLs are handled in applications. A noteworthy change in this area relates to the deprecation of the `stringByAddingPercentEscapesUsingEncoding` method. This outdated method has been replaced with `stringByAddingPercentEncodingWithAllowedCharacters`, which provides a more robust and flexible way to handle URLs and character encodings. This article delves into these changes, providing insights, examples, and useful information for developers looking to modernize their applications.

Background: URL Encoding

URL encoding, also known as percent encoding, is a method to encode information in a Uniform Resource Identifier (URI). It replaces characters that are not allowed or have a special meaning in a URL with a '%' sign followed by two hexadecimal digits. For example, spaces are replaced with `%20` or `+`, and special characters like `&` are also encoded.

Method Deprecation

In earlier versions of iOS and macOS, developers commonly used `stringByAddingPercentEscapesUsingEncoding` to encode strings to be included in URLs. This method took an NSStringEncoding value and returned a new string where certain characters were replaced by the corresponding escape sequences. Despite its utility, this method is limited due to its inability to handle some of the more complex rules associated with URL encoding.

With the release of iOS 9, Apple deprecated this method in favor of `stringByAddingPercentEncodingWithAllowedCharacters`, providing a more flexible and comprehensive encoding solution.

Replacement: `stringByAddingPercentEncodingWithAllowedCharacters`

Benefits

• Customizable Allowed Characters: Unlike its predecessor, this method allows for the specification of a custom set of characters that are allowed unescaped in the encoded URL. This gives developers more control over the encoding process.
• Improved Flexibility: It facilitates better handling of various character sets beyond simple ASCII, which is particularly useful for internationalization efforts or special URL requirements.

Usage

The replacement method takes advantage of a `CharacterSet` to determine which characters are not to be percent-encoded. Developers can create custom `CharacterSet` objects or utilize predefined ones, like `URLQueryAllowedCharacterSet`, to suit specific needs.

Example

Below is a usage example demonstrating how to encode a URL component using `stringByAddingPercentEncodingWithAllowedCharacters`.

• Character Set Selection: The `URLQueryAllowedCharacterSet` allows all characters that are valid within the query component of a URL.
• Percent Encoding: Unallowed characters in `urlComponent` are percent-encoded, making it safe to use within URLs.